1. Field of the Invention
The present invention relates a plunger pump apparatus including a pump having a plunger reciprocated by an eccentric cam portion provided on a pump drive shaft and provided in a body and an electric motor provided on one side of the body in such a manner as to drive to rotate the pump drive shaft.
2. Description of the Background Art
There is known in Japanese Patent Unexamined Publication No. JP-A-1-290977, a plunger pump apparatus in which as a venting measure for the electric motor in the plunger pump apparatus as described above, a grommet is held between a motor casing of the electric motor and the body, and a vent passage is provided in the grommet which establishes a communication between the inside of the electric motor and the outside.
Incidentally, in the conventional plunger pump apparatus, a change in volume of air due to a change in temperature is not taken into consideration. Namely, when the pump apparatus, which is in a warmed up state due to operation, is submerged, air within the electric motor is caused to contract due to cooling in addition to the application of water pressure, and the amount of water penetrating into the electric motor from the vent passage at the time of the submergence is increased due to the contraction of air, resulting in a possibility that the inside of the electric motor is submerged.
There is also already known, for example, in Japanese Patent Unexamined Publication No. JP-A-2-249749, a plunger pump apparatus in which a needle baring, functioning as a bearing unit, is fitted on an eccentric cam portion of a pump drive shaft and a plunger is brought into sliding contact with the needle bearing at one end thereof.
Incidentally, when compared to ball bearings, needle bearings are high in production cost and tend to generate large vibration and loud noise, and hence, there have existed demands for ball bearings in place of the needle bearings in order to solve the problems inherent in the latter. On the other hand, in plunger pump apparatuss, it is desired that a sliding fitting portion of a plunger into a pump housing is made as diametrically small as possible while the stroke is extended from the viewpoint of efficiency and strength.
However, when a needle bearing is simply replaced with a single ball bearing, there is caused a problem with durability, and therefore, when a ball bearing is used, a plurality of ball bearings need to be arranged in parallel. In ball bearings of a size which can be fitted on the eccentric cam portion on the pump drive shaft, since a distance between balls of ball bearings of the plurality of ball bearings which lie at both ends of the ball bearing arrangement direction becomes relatively long, when one end portion of the plunger which is small in diameter is brought into direct abutment, with outer rings of the plurality of ball bearings, the end portion of the plunger abuts with outer surfaces of the outer rings inwards of balls of the ball bearings lying at both the ends of the ball bearing arrangement direction, and the outer rings of the ball bearings are inclined relative to the axis of the pump drive shaft, whereby there is caused a problem that the operation of the pump drive shaft at the eccentric cam portion becomes unstable. The problem becomes remarkable in a combination of the pair of ball bearings which are arranged in parallel and the plunger which is brought into abutment with the middle portion of the pair of ball bearings so arranged.